The present invention relates to a novel organocyclotetrasiloxane and a room temperature curable composition containing the same.
There are known several types of room temperature curable silicone rubber compositions capable of giving a rubbery elastomer when kept standing under atmospheric condition. They are classified according to the storability of the ready-mixed composition into so-called two-package type ones and one-package type ones, the composition of the former type being stored in two separate packages each containing different ingredient or ingredients from the other to be blended together directly before application and the composition of the latter type being storable in one package containing all of the ingredients of the composition blended together in advance.
The room temperature curable silicone rubber compositions are also classified into several types according to the mechanism of the crosslinking reaction by which the composition is cured. Most of the crosslinking reactions proceed by the mechanism of condensation reaction between functional groups and the condensation products produced by the reaction may be an amine, a hydroxylamine, an oxime, a carboxylic acid, e.g. acetic acid, or an alcohol. The condensation products other than the alcohols are all toxic or corrosive so that application of the silicone rubber compositions curable with formation of such noxious condensation products is greatly limited unless good ventilation is provided in the working place. On the other hand, the room temperature curable silicone rubber compositions curable by the dealcoholation condensation are free from the problem of noxious gaseous condensation products produced by the crosslinking reaction although the compositions of this type have other disadvantages of poor storability of the ready mixed composition, relatively long curing time and brittleness or fragility of the cured product.
Furthermore, the curing catalysts and the curing accelerators formulated in these room temperature curable silicone rubber compositions also cause some problems. For example, titanium alkoxide compounds as a curing accelerator and certain metal salts of carboxylic acids used as a curing catalyst in the compositions curable by producing acetic acid or an oxime as the condensation product remain in the cured product and cause coloration and decrease in the mechanical properties thereof in addition to the problem of toxicity in some cases.
Accordingly, there have been recently developed improved room temperature curable silicone rubber compositions in which the crosslinking reaction proceeds by the condensation reaction with formation of a ketone compound as the condensation product when the composition is kept in a moisture-containing atmosphere (see, for example, Japanese Patent Publications Nos. 51-39274, 51-39673 and 54-44699). The compositions of this type have no problems in respect of the corrosiveness and adhesion to the substrate surface but they are disadvantageous due to the not always satisfactory ultimate elongation of the cured rubbery elastomer.